Structural and expression analyses of two vitellogenin genes in the carp, Cyprinus carpio

Genome-Wide Identification, Expression and Response to Estrogen of Vitellogenin Gene Family in Sichuan Bream (Sinibrama taeniatus)

To enhance our understanding of teleost reproductive physiology, we identified six Sichuan bream (Sinibrama taeniatus) vitellogenin genes (vtg1-6) and characterized their sequence structures. We categorized them into type Ⅰ (vtg1,4,5 and 6), type Ⅱ (vtg2) and type Ⅲ (vtg3) based on differences in their subdomain structure. The promoter sequence of vtgs has multiple estrogen response elements, and their abundance appears to correlate with the responsiveness of vtg gene expression to estrogen. Gene expression analyses revealed that the vitellogenesis of Sichuan bream involves both heterosynthesis and autosynthesis pathways, with the dominant pathway originating from the liver. The drug treatment experiments revealed that 17β-estradiol (E2) tightly regulated the level of vtg mRNA in the liver. Feeding fish with a diet containing 100 μg/g E2 for three weeks significantly induced vtg gene expression and ovarian development, leading to an earlier onset of vitellogenesis. Additionally, it was observed that the initiation of vtg transcription required E2 binding to its receptor, a process primarily mediated by estrogen receptor alpha in Sichuan bream. The findings of this study provide novel insights into the molecular information of the vitellogenin gene family in teleosts, thereby contributing to the regulation of gonadal development in farmed fish.

Structural modeling and gene expression analysis of phosvitinless vitellogenin (vgc) in the Indian freshwater murrel, Channa punctatus (Bloch, 1793)

Vitellogenin (Vg) is a female-specific egg-yolk precursor protein, synthesized in the liver of fish in response to estrogens. In the present study, complete gene of phosvitinless vitellogenin (vgc) was sequenced, its 3D structure was predicted and validated by web-based softwares. The complete nucleotide sequence of vgc was 4126 bp which encodes for 1272 amino acids and showed the presence of three conserved domains viz. LPD_N, DUF1943 and DUF1944. The retrieved amino acid sequence of VgC protein was subjected to in silico analysis for understanding the structural and functional properties of protein. mRNA levels of multiple vg genes have also been quantified during annual reproductive cycle employing qPCR. A correlation has been observed between seasonal changes in gonadosomatic index with estradiol levels and hepatic expression of three types of vg genes (vga, vgb, vgc) during ovarian cycle of murrel. During preparatory phase, when photoperiod and temperature are low; low titre of E2 in blood induces expression of vgc gene. A rapid increase in the levels of E2 favours induction of vgb and vga genes in liver of murrel during early pre-spawning phase when photoperiod is long and temperature is high in nature. These results suggest that among three vitellogenin proteins, VgC is synthesized earlier than VgA and VgB during oogenesis.

Silencing of novel TtVtg6-like induced ovarian cell apoptosis in ancient chelicerate Tachypleus tridentatus

Vitellogenin (Vtg) serves as the precursor of yolk protein and exhibits widespread distribution in tissues, including in the ovary of both vertebrates and invertebrates. Vtg plays a critical role in facilitating oocyte maturation and embryonic development following oviposition. In this study, we have successfully elucidated the complete transcript sequence of TtVtg6-like from an ancient chelicerate Tachypleus tridentatus. The TtVtg6-like transcript encompassed a length of 4887 bp and encoded 1629 amino acids residues. Notably, TtVtg6-like was found to contain 25 exons. Furthermore, the molecular weight and isoelectric point of TtVtg6-like were determined to be 191.6 KDa and 6.73, respectively. Subsequent mRNA expression analysis demonstrated the specific expression of TtVtg6-like in ovary and yellow connective tissue. In addition, TtVtg6-like was located and distributed in both ovary and yellow connective tissue. Intriguingly, employing an siRNA approach to silence TtVtg6-like resulted in a decrease in TtVtg6-like transcription levels. Concomitantly, TtVtg6-like silencing led to increase production of ROS, ultimately resulting in DNA damage and cell apoptosis within the ovarian primary cell. The induction of apoptosis ovarian primary cells due to TtVtg6-like silencing was further corroborated through TUNEL assay and flow cytometry analysis. Overall, our findings underscore the significance of TtVtg6-like in ovarian cell development, revealing its potential association with ovarian cell apoptosis. Consequently, the insights gained from this study contribute to the future exploration of vitellogenesis and ovarian development in T. tridentatus.

Molecular cloning, characterisation and expression analysis of the vitellogenin genes vtgAo1 and vtgC during ovarian development in Chinese hook snout carp Opsariichthys bidens

Vitellogenesis is essential for oocyte maturation. Vitellogenin (Vtg), a yolk precursor protein, plays an important role in oogenesis and vitellogenesis. Chinese hook snout carp Opsariichthys bidens is an economically important freshwater fish in China whose reproductive and developmental biology are not well understood. In this study, we undertook histological analysis to examine ovary development and oogenesis in O. bidens. The ovaries were divided into Stages II-V and oocytes were divided into perinuclear oocytes, cortical alveoli oocytes, vitellogenic oocytes and mature oocytes. Full-length cDNA sequences were cloned of two vtg genes from the liver of O. bidens, namely Ob-vtgAo1 and Ob-vtgC. Ob-vtgAo1 and Ob-vtgC cDNA are made up of 4136 and 4392 bases respectively and encode proteins containing 1335 and 1250 amino acids respectively. Ob-vtgAo1 contains three yolk protein domains: lipovitellin heavy chain (LvH), phosvitin (Pv) and lipovitellin light chain (LvL), whereas Ob-VtgC contains LvH and LvL, which are incomplete Vtgs. Ob-vtgAo1 and Ob-vtgC mRNA expression was significantly higher in the liver of O. bidens than in all other tissues. In oocytes of Stage II-III ovaries, yolk granules are almost absent and ovarian and hepatic Ob-vtgAo1 and Ob-vtgC expression is low. At Stage IV, the oocyte is filled with yolk granules and ovarian and hepatic Ob-vtgAo1 and Ob-vtgC expression is significantly increased. Collectively, these findings help us better understand vitellogenesis in O. bidens.

Heavy chain (LvH) and light chain (LvL) of lipovitellin (Lv) of zebrafish can both bind to bacteria and enhance phagocytosis

Lipovitellin (Lv) is an apoprotein in oviparous animals. Lv consists of a heavy chain (LvH) and a light chain (LvL) which are traditionally regarded as energy reserves for developing embryos. Recently, Lv has been shown to be involved in immune defense of developing embryos in fish. However, it remains unknown if each of LvH and LvL possesses immune activity; and if so, whether or not they function similarly. Here we clearly demonstrated that recombinant LvH (rLvH) and LvL (rLvL) from zebrafish vg1 gene bound to both the Gram-negative bacteria Escherichia coli and Vibrio anguillarum and the Gram-positive bacteria Staphylococcus aureus and Micrococcus luteus as well as the pathogen-associated molecular patterns LPS, LTA and PGN. In addition, both rLvH and rLvL were able to enhance the phagocytosis of bacteria E. coli and S. aureus by macrophages. All these data suggest that both LvH and LvL, in addition to being energy reserves, are also maternal immune-relevant factors capable of interacting with invading bacteria in zebrafish embryos/larvae.

Regulation of vitellogenin (vtg1) and estrogen receptor (er) gene expression in zebrafish (Danio rerio) following the administration of Cd²⁺ and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

We evaluated the individual and joint estrogenic effects of cadmium (Cd(2+)) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the zebrafish liver (ZFL) cell line, zebrafish embryo, larvae and the liver of adult zebrafish. The mRNA expression of vtg1 was inhibited by Cd(2+), but unaffected by TCDD in ZFL cells. Similar changes in the mRNA levels of ERα, ERβ1, ERβ2 and GPER (G protein coupled estrogen receptor) in ZFL cells were also observed. Deletion mutants of vtg1 gene promoters were constructed to investigate transcriptional regulation, and we found that all of the constructs failed to respond to TCDD or Cd(2+). However, after co-transfection with a vtg1 promoter-luciferase construct to the ERα, ERβ1, ERβ2 and GPER expression vectors, decreased luciferase activity was observed in the ERα co-transfection group after treatment with Cd(2+), suggesting that ERα participates in vtg1 transcriptional regulation and is affected by Cd(2+). Differences in the regulation of the mRNA levels of these genes were also observed between different developmental stages and between the livers of male and female zebrafish.

Immune-Relevant and Antioxidant Activities of Vitellogenin and Yolk Proteins in Fish

Vitellogenin (Vtg), the major egg yolk precursor protein, is traditionally thought to provide protein- and lipid-rich nutrients for developing embryos and larvae. However, the roles of Vtg as well as its derived yolk proteins lipovitellin (Lv) and phosvitin (Pv) extend beyond nutritional functions. Accumulating data have demonstrated that Vtg, Lv and Pv participate in host innate immune defense with multifaceted functions. They can all act as multivalent pattern recognition receptors capable of identifying invading microbes. Vtg and Pv can also act as immune effectors capable of killing bacteria and virus. Moreover, Vtg and Lv are shown to possess phagocytosis-promoting activity as opsonins. In addition to these immune-relevant functions, Vtg and Pv are found to have antioxidant activity, which is able to protect the host from oxidant stress. These non-nutritional functions clearly deepen our understanding of the physiological roles of the molecules, and at the same time, provide a sound basis for potential application of the molecules in human health.

Immune-Relevant and Antioxidant Activities of Vitellogenin and Yolk Proteins in Fish

Vitellogenin (Vtg), the major egg yolk precursor protein, is traditionally thought to provide protein- and lipid-rich nutrients for developing embryos and larvae. However, the roles of Vtg as well as its derived yolk proteins lipovitellin (Lv) and phosvitin (Pv) extend beyond nutritional functions. Accumulating data have demonstrated that Vtg, Lv and Pv participate in host innate immune defense with multifaceted functions. They can all act as multivalent pattern recognition receptors capable of identifying invading microbes. Vtg and Pv can also act as immune effectors capable of killing bacteria and virus. Moreover, Vtg and Lv are shown to possess phagocytosis-promoting activity as opsonins. In addition to these immune-relevant functions, Vtg and Pv are found to have antioxidant activity, which is able to protect the host from oxidant stress. These non-nutritional functions clearly deepen our understanding of the physiological roles of the molecules, and at the same time, provide a sound basis for potential application of the molecules in human health.

Functional analysis of domain of unknown function (DUF) 1943, DUF1944 and von Willebrand factor type D domain (VWD) in vitellogenin2 in zebrafish

Vitellogenin (Vg), the precursor of egg-yolk proteins in all oviparous organisms, shares a similar domain structure combination. In most cases, Vg contains the Vitellogenin_N domain, the domain of unknown function (DUF) 1943, and the von Willebrand factor type D domain (VWD), which are present in different forms of Vg from both vertebrates and invertebrates. Occasionally, a DUF1944 domain is also present in between DUF1943 and VWD in some Vg proteins of vertebrates. Recent studies have shown that Vg participates in immune defense of host with multiple functions. However, whether all Vg proteins encoded by different vg genes play an immune role is unknown. In addition, the correlation of different domains in Vg with the multiple immune functions remains completely unclear. Here we demonstrated clearly that recombinant proteins, rDUF1943, rDUF1944 and rVWD from zebrafish Vg2 interacted with both the Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus and the Gram-negative bacteria Escherichia coli and Vibrio anguillarum, as well as their signature components LTA and LPS. Moreover, both rDUF1943 and rDUF1944 promoted the phagocytosis of E. coli and S. aureus by carp macrophages. These suggest that both DUF1943 and DUF1944 as well as VWD may contribute to the function of Vg as a pattern recognition receptor, and DUF1943 and DUF1944 also contribute to the function of Vg as an opsonin. This study also opens a new angle for identification of function of genes of unknown function, which have the domains DUF1943 and DUF1944.

Meta-type analysis of dopaminergic effects on gene expression in the neuroendocrine brain of female goldfish

Dopamine (DA) is a major neurotransmitter important for neuroendocrine control and recent studies have described genomic signaling pathways activated and inhibited by DA agonists and antagonists in the goldfish brain. Here we perform a meta-type analysis using microarray datasets from experiments conducted with female goldfish to characterize the gene expression responses that underlie dopaminergic signaling. Sexually mature, pre-spawning [gonadosomatic index (GSI) = 4.5 ± 1.3%] or sexually regressing (GSI = 3 ± 0.4%) female goldfish (15-40 g) injected intraperitoneally with either SKF 38393, LY 171555, SCH 23390, sulpiride, or a combination of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and α-methyl-p-tyrosine. Microarray meta-type analysis identified 268 genes in the telencephalon and hypothalamus as having reciprocal (i.e., opposite between agonism and antagonism/depletion) fold change responses, suggesting that these transcripts are likely targets for DA-mediated regulation. Noteworthy genes included ependymin, vimentin, and aromatase, genes that support the significance of DA in neuronal plasticity and tissue remodeling. Sub-network enrichment analysis (SNEA) was used to identify common gene regulators and binding proteins associated with the differentially expressed genes mediated by DA. SNEA analysis identified gene expression targets that were related to three major categories that included cell signaling (STAT3, SP1, SMAD, Jun/Fos), immune response (IL-6, IL-1β, TNFs, cytokine, NF-κB), and cell proliferation and growth (IGF1, TGFβ1). These gene networks are also known to be associated with neurodegenerative disorders such as Parkinsons' disease, well-known to be associated with loss of dopaminergic neurons. This study identifies genes and networks that underlie DA signaling in the vertebrate CNS and provides targets that may be key neuroendocrine regulators. The results provide a foundation for future work on dopaminergic regulation of gene expression in fish model systems.

Novel recombinant monoclonal antibodies for vitellogenin assays in cyprinid fish species

Various polyclonal and monoclonal antibodies have been developed for vitellogenin (Vtg) bioassays in different aquatic species. Preparation of these reagents is time-consuming and expensive. In the present study, a phage-displayed, recombinant, single-chain variable fragment (scFv) format antibody library was constructed using splenic mRNA from non-immunized mice. After 3 rounds of panning, 3 scFv antibodies with specificity for the highly conserved N-terminal region of cyprinid fish Vtg were isolated. One of these, antibody H4, bound purified Vtg from common carp Cyprinus carpio, zebrafish Danio rerio and Chinese rare minnow Gobiocypris rarus with similar affinities and detected Vtg in zebrafish plasma samples. This study provides a simple, low cost Vtg bioassay for plasma samples from a variety of cyprinid fish.

Cloning, expression, and induction by 17-beta estradiol (E2) of a vitellogenin gene in the white cloud mountain minnow Tanichthys albonubes

Vitellogenins (Vtgs), the precursors for the yolk proteins, are very important for the embryonic development of teleosts, and have also been studied extensively as biomarkers for environmental estrogenic mimics. The cDNA for a Vtg was isolated from the liver of the female white cloud mountain minnow (Tanichthys albonubes) by 3'- and 5'-RACE methods. It is 4,171 bp in full length, and encodes a putative protein of 1,326 amino acids. This putative Vtg, designated as wcmmVtg, contains complete portions of LVI and PV, but lacks the C-terminal half of LVII and thus belongs to type I vitellogenin. In addition to the liver of the female fish, wcmmVtg was also shown to be expressed in the ovary. During ovarian development, the mRNA expression of wcmmVtg in both the liver and ovary was continuously increased from the previtellogenic to late vitellogenic stages, but then decreased significantly at post-spawning stage. In the male fish, expression of wcmmVtg mRNA was induced in the liver by treatment with E2 (10 and 100 ng/l) for 14 days. These results suggest that the Vtg originated from the ovary of the white cloud mountain minnow may also contribute to the accumulation of yolk proteins during oocyte growth, and that the male white cloud mountain minnow is sensitive to the estrogenic treatment in terms of Vtg mRNA expression, which could also be applied to monitor the environmental estrogenic mimics.

Evolution and differential expression of a vertebrate vitellogenin gene cluster

Background

The multiplicity or loss of the vitellogenin (vtg) gene family in vertebrates has been argued to have broad implications for the mode of reproduction (placental or non-placental), cleavage pattern (meroblastic or holoblastic) and character of the egg (pelagic or benthic). Earlier proposals for the existence of three forms of vertebrate vtgs present conflicting models for their origin and subsequent duplication.

Results

By integrating phylogenetics of novel vtg transcripts from old and modern teleosts with syntenic analyses of all available genomic variants of non-metatherian vertebrates we identify the gene orthologies between the Sarcopterygii (tetrapod branch) and Actinopterygii (fish branch). We argue that the vertebrate vtg gene cluster originated in proto-chromosome m, but that vtg genes have subsequently duplicated and rearranged following whole genome duplications. Sequencing of a novel fourth vtg transcript in labrid species, and the presence of duplicated paralogs in certain model organisms supports the notion that lineage-specific gene duplications frequently occur in teleosts. The data show that the vtg gene cluster is more conserved between acanthomorph teleosts and tetrapods, than in ostariophysan teleosts such as the zebrafish. The differential expression of the labrid vtg genes are further consistent with the notion that neofunctionalized Aa-type vtgs are important determinants of the pelagic or benthic character of the eggs in acanthomorph teleosts.

Conclusion

The vertebrate vtg gene cluster existed prior to the separation of Sarcopterygii from Actinopterygii >450 million years ago, a period associated with the second round of whole genome duplication. The presence of higher copy numbers in a more highly expressed subcluster is particularly prevalent in teleosts. The differential expression and latent neofunctionalization of vtg genes in acanthomorph teleosts is an adaptive feature associated with oocyte hydration and spawning in the marine environment.